Today, it is common practice to utilize lasers in dermatological treatments by the use of long single pulses (of about a few milliseconds) at a constant power or a train of pulses. In most such cases, this kind of treatment is accompanied with the application of local cooling of the area of the skin tissue which is treated. This method, although considered effective for many skin types, is usually not considered safe for treating people with dark skin as it might produce severe burns.
FIGS. 1A and 1B represent simulations of a laser assisted hair removal process with skin type IV (FIG. 1A) and skin type VI (FIG. 1B). Skin types are conventionally categorized as levels I through VI in dermatological practice using the Fitzpatrick scale, the higher the number being the darker the skin tone. In FIGS. 1A and 1B, the temperature of the hair follicle as well as the temperature of the epidermis at various levels can be seen. The treatment parameters that were used in the simulation for skin type IV have been proven to be both safe and effective. The obtained temperatures in the hair follicle are very high while maintaining the skin temperature at acceptable temperature levels. When trying to obtain even smaller temperature levels of hair follicle in type VI skin (which additionally has the disadvantage of less efficacy), the epidermis temperature increased to dangerous levels, as shown in FIG. 1B.
In another known approach, known as bulk heating, the laser system made to emit a continuous pulse sequence (such as, for example, 10 Hz 20 ms); the clinician glides the treatment head over an extended treated area, causing a gradual temperature increase in this area by repeated “visits” at the same spots. This method is typically applied with very mild cooling. Although safer than the method discussed previously when treating dark skin, it is considered less effective, especially when treating light hair or when trying to treat specific glands.